Method and system for forwarding data between a plurality of provider ethernet networks

ABSTRACT

The present invention discloses a method and a system for forwarding data between provider Ethernet networks, wherein a first provider Ethernet network is the first provider Ethernet network in a path through which a first data packet is transmitted, and a second provider Ethernet network is the last provider Ethernet network in the path. The method includes using network addresses of the first provider Ethernet network and the second provider Ethernet network as a source address and a destination address of an outer MAC header with which the first data packet is encapsulated when the first data packet is transmitted between the first provider Ethernet network and the second provider Ethernet network; and decapsulating the first data packet and forwarding the decapsulated data packet to the second client network after the first data packet is forwarded to the second provider Ethernet network.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Patent ApplicationNo. PCT/CN2007/070424, filed Aug. 6, 2007, which claims priority toChinese Patent Application No. 200610062046.1, filed Aug. 9, 2006, bothof which are hereby incorporated by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to the technical field of Ethernetnetwork, in particular to a method and a system for forwarding databetween a plurality of provider Ethernet networks.

BACKGROUND OF THE INVENTION

Ethernet network technology not only has been widely applied in localarea network environments of enterprises, but also intereststelecommunication providers increasingly in building provider Ethernetnetworks, due to its advantages such as low cost, mature standard andflexible techniques. An important reason among others is that theEthernet network technology has advantages such as low cost andstatistical multiplexing function. However, due to limitations ofconventional Ethernet network techniques, such as poor extensibility andinteroperability, a series of problems occur when extending an Ethernetnetwork application to a metropolitan area network.

In order to solve the extensibility of the Ethernet network, thoseskilled in the art proposed a technical scheme called MAC-in-MAC (MediaAccess Control). In the MAC-in-MAC technical scheme, when a data packetof a client arrives at a Provider Edge Bridge (PEB), the PEBencapsulates the data packet with an outer MAC header, a source addressof which is a MAC address of the present PEB and a destination addressof which is a MAC address of a destination PEB. To encapsulate with theouter MAC header, it is necessary for the PEB to perform addresslearning according to the source address of the outer MAC header of thereceived data packet to obtain mapping between a destination address ofthe client and the address of the destination PEB. The MAC-in-MACtechnical scheme enables an internal bridge in a provider network tomask the MAC address of a network of the client.

On the basis of the MAC-in-MAC technical scheme, IEEE has established anew standard 802.1ah, and an 802.1ah-based network is referred to as aProvider Backbone Bridged Network (PBBN). However, the standard 802.1 ahis under refinement, and there is no mature solution for forwarding datain a multi-PBBN environment yet.

At present, there exist two technical schemes on the basis of tieredinterconnection and peer-to-peer interconnection in the conventional artfor solving the data forwarding in the multi-PBBN environment.Hereunder, the two technical schemes will be further described in detailwith reference to the accompanying drawings.

In a tiered interconnection model, a plurality of PBBNs are divided intoseveral levels. The PBBN on an upper level serve as a service level fora PBBN on a lower level to provide a transparent transmission servicefor data transmission between the PBBNs on the lower levels.

With reference to FIG. 1, a Provider Bridged Network (PBN) on a lowestlevel is a provider network constructed on the basis of a Q-in-Q schemein IEEE 802.1ad, and is adapted to provide an Ethernet network servicefor a client bridged network. The Q-in-Q scheme extends the Ethernetnetwork and achieves isolation between a provider VLAN and a clientVLAN. A typical message format in the PBN is as follows.

C-DA C-SA S-TAG C-TAG Client-Data FCSWhere the C-DA is the destination address of a client, namely, theDestination Address (DA) of data packets of the client; the C-SA is thesource address of the client, namely, the Source Destination (SA) of thedata packets of the client; the S-TAG is TAG of a VLAN in the PBN; theC-TAG is TAG of the VLAN carried in the data packets of the client; andthe FCS is a frame check sequence.

The three PBBNs on the upper levels are a provider backbone Ethernetnetwork constructed on the basis of the MAC-in-MAC scheme in the IEEE802.1 ah, and are mainly adapted to interconnect a plurality of thePBNs. A typical message format in the PBBN is as follows.

B-DA B-SA B-TAG I-TAG Client-Data FCS

Where the B-DA (Provider Backbone Destination Address) is thedestination address of the provider backbone bridge, namely, thedestination address for the outer MAC header; the B-SA (ProviderBackbone Source Address) is the source address of the provider backbonebridge, namely, the source address for the outer MAC header; the B-TAG(Backbone VLAN TAG) is a tag of the backbone VLAN; the I-TAG (ServiceInstance TAG) is a tag of a service instance; and Client-Data here is adata packet of a complete format in the PBN.

According to planning, the three PBBNs can be divided into two levels ofLevel 1 and Level 2 by the provider. A plurality of PBBNs on Level 1 areconnected by the PBBN on Level 2. Data is transmitted between the twoPBBNs on Level 1 through the transparent transmission of the PBBN onLevel 2. The PBBN on Level 2 treats a data packet from Level 1 at aningress node as a payload. The data packet from Level 1 is encapsulatedwith the outer MAC header for the present level, and an Ethernet networkdata packet encapsulated is forwarded on the present level in accordancewith the outer MAC header. At the egress node of Level 2, the Ethernetdata packet is decapsulated to remove the outer MAC header for thepresent level, and is forwarded to the other PBBN on Level 1.

It can be seen from the above description of the tiered interconnectiontechnical scheme that, it is necessary for the Ethernet data packet fromLevel 1 to be encapsulated with information of an outer MAC header forLevel 2. That is, it is necessary for a data packet from a PBN to beencapsulated with information of two levels of MAC header, so that thenumber of levels of encapsulation is increased, which lowers dataforwarding efficiency.

In order to avoid the lowering of the forwarding efficiency, apeer-to-peer interconnection solution can be used. With reference toFIG. 2, a schematic diagram of a peer-to-peer interconnection network isshown in FIG. 2, in which PBBN1 and PBBN2 are two provider backbonebridged networks connected in a peer-to-peer manner. In a peer-to-peerinterconnection model, when a data packet enters PBBN1 through aningress node PBB1 (Provider Backbone Bridge 1), PBB1 encapsulates thedata packet with an outer MAC header. When the data packet passesthrough two PBBNs via PBB2 and PBB3, the Ethernet network data packet isnot encapsulated with a new outer MAC header, instead, the old outer MACheader is replaced with a new outer MAC header. In order to preventaddress information of specific network devices (such as PBB2 and PBB3)in the present provider Ethernet network from exposing to other providerEthernet networks, the addresses contained in the outer MAC header usedduring the transmission of the data packet from PBB2 to PBB3 are usuallynot real addresses of the two edge nodes PBB2 and PBB3, instead arepseudo address information of PBB2 and PBB3. In that case, it needs toconfigure mapping relationship between respective real addresses andpseudo addresses at external network network interfaces (E-NNI) for PBB2and PBB3, and such mapping relationship is usually configured on thebasis of the I-TAG carried in a message. Then, the addresses in theouter MAC header must be translated and replaced (translated between thepseudo addresses and the real address) on PBB2 and PBB3 respectively. Itcan be seen that, to establish an inter-domain path between a pluralityof provider Ethernet networks for data packets, it needs to performaddress replacement at edge nodes, and mapping relationship must bedetermined to accomplish the replacement process. However, theestablishment of such mapping relationship needs to be implemented bymeans of complex configuration when a service is established.Furthermore, since length that needs to be matched is long (at leastincluding I-TAG, real addresses and pseudo addresses), it is difficultfor the looking up of a table to be implemented by means of hardware.

SUMMARY OF THE INVENTION

The present invention provides a method and a system for forwarding databetween a plurality of provider Ethernet networks, which neither lowersthe forwarding efficiency, nor needs to establish an inter-domain pathby means of complex configuration when transmitting data between aplurality of PBBNs.

The present invention provides a method for forwarding data between aplurality of provider Ethernet networks, wherein a first providerEthernet network is the first provider Ethernet network in a paththrough which a first data packet is transmitted from a first clientnetwork to a second client network, and a second provider Ethernetnetwork is the last provider Ethernet network in the path through whichthe first data packet is transmitted. The method includes using anetwork address of the first provider Ethernet network and a networkaddress of the second provider Ethernet network as a source address anda destination address of an outer MAC header with which the first datapacket is encapsulated when the first data packet is transmitted betweenthe first provider Ethernet network and the second provider Ethernetnetwork; and decapsulating, by the second provider Ethernet network, thefirst data packet and forwarding the decapsulated data packet to thesecond client network after the first data packet is forwarded to thesecond provider Ethernet network.

The present invention further provides a system for forwarding databetween a plurality of provider Ethernet networks. The system includes afirst provider Ethernet network connected to a first client network anda second provider Ethernet network connected to a second client network,wherein the first provider Ethernet network is the first providerEthernet network in a path through which a first data packet istransmitted from the first client network to the second client network,and the second provider Ethernet network is the last provider Ethernetnetwork in the path through which the first data packet is transmitted.The first provider Ethernet network includes a first outer MAC headerprocessing unit adapted to encapsulate the first data packet with anouter MAC header according to a network address of the first providerEthernet network and a network address of the second provider Ethernetnetwork; and a forwarding unit adapted to forward the first data packetprocessed by the first outer MAC header processing unit towards thesecond provider Ethernet network. The second provider Ethernet networkincludes a second outer MAC header processing unit adapted todecapsulate the outer MAC header of the first data packet from the firstprovider Ethernet network; and a second forwarding unit adapted toforward the first data packet processed by the second outer MAC headerprocessing unit to the second client network.

The present invention further provides a system for forwarding databetween a plurality of provider Ethernet networks. The system includes afirst provider Ethernet network connected to a first client network anda second provider Ethernet network connected to a second client network,wherein the first provider Ethernet network is the first providerEthernet network in a path through which a first data packet istransmitted from the first client network to the second client network,and the second provider Ethernet network is the last provider Ethernetnetwork in the path through which the first data packet is transmitted.An edge node of the provider Ethernet network includes a mappingrelationship storage unit adapted to store mapping relationship betweena client source address and a source address of an outer MAC header ofthe first data packet received by the edge node; and an outer MAC headerprocessing unit adapted to replace the source address and a destinationaddress of the outer MAC header of the first data packet according tomapping information provided by the mapping relationship storage unit.The outer MAC header processing unit at an egress node of the firstprovider Ethernet network is adapted to replace the source address ofthe outer MAC header of the first data packet with a network address ofthe first provider Ethernet network. The outer MAC header processingunit at an ingress node of the second provider Ethernet network isadapted to query and obtain an address of an egress node of the secondprovider Ethernet network corresponding to the client destinationaddress of the first data packet according to information provided bythe mapping relationship storage unit, and to replace the source addressand the destination address of the outer MAC header of the first datapacket with the address of the ingress node of the second providerEthernet network and the address of an egress node of the secondprovider Ethernet network.

It can be seen from the above description of the embodiments of thepresent invention that, when a data packet is forwarded betweendifferent provider Ethernet networks, the network addresses of the firstprovider Ethernet network and the last provider Ethernet network in thetransmission path are used as the B-SA and B-DA in the outer MAC headerof the data packet. Then, the data packet is decapsulated by the lastprovider Ethernet network and forwarded to the destination clientnetwork. Therefore, on the one hand, it only needs to be encapsulatedwith a single layer of MAC header according to the present invention,which will not lower the forwarding efficiency. On the other hand, sincethe network address of the provider Ethernet network, instead of theaddresses of the edge node of the provider Ethernet network and the edgenode at the opposite end, are used when the data packet is transmittedbetween different provider Ethernet networks, it is unnecessary toconfigure the complex mapping relationship between the real address andthe pseudo address for the respective edge nodes, which simplifies theestablishment of the inter-domain path and can be achieved easily.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a tiered-interconnection network model;

FIG. 2 is a schematic diagram of a peer-to-peer interconnection networkmodel;

FIG. 3 is a schematic diagram of a network model for forwarding databetween a plurality of PBBNs according to an embodiment of the presentinvention;

FIG. 4 is a schematic diagram of node types in a PBBN according to anembodiment of the present invention;

FIG. 5 is a flow diagram for processing a data packet received through aUNI by an ingress node of a PBBN according to an embodiment of thepresent invention;

FIG. 6 is a flow diagram for processing a data packet received throughan E-NNI by an ingress node of a PBBN according to an embodiment of thepresent invention;

FIG. 7 is a flow diagram for processing a data packet by an egress nodeof a PBBN according to an embodiment of present invention; and

FIG. 8 is a structural representation of an embodiment of a system forforwarding data between a plurality of provider Ethernet networksaccording to the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

An embodiment of the present invention is applicable to a circumstancewhere a plurality of PBBNs are interconnected. That is, an embodiment ofthe present invention provides a method and a system for forwarding datain a network with a plurality of interconnected PBBNs.

A provider assigns a MAC address to each PBBN managed per se as aprovider network address. When a data packet is transmitted from a PBBNto another PBBN, the provider network address assigned is used as asource address and a destination address in an outer MAC header. Anintermediate node in data packet transmission path establishes a dataforwarding table and determines an inter-domain path by means of aself-learning mechanism according to the provider network address,thereby simplifying configuration of the inter-domain path.

Specifically, when a data packet enters a first PBBN from a clientnetwork, the data packet is encapsulated with an outer MAC header at aningress node. A source address in the outer MAC header is the address ofthe ingress node (specifically, may be the address of the ingress nodeper se, or the address of an ingress port through which the data packetenters the edge node), and a destination address is the network addressof a second PBBN (namely, a PBBN that is directly connected to adestination client network) obtained by looking up a mapping table. Whenthe data packet exits the first PBBN, a B-SA in the data packet isreplaced with the network address of the first PBBN at an egress node.When the data packet enters the second PBBN, at the ingress node of thesecond PBBN, a B-SA in the data packet is replaced with the address ofthe ingress node of the second PBBN, and a B-DA is replaced with theaddress of the egress node of the second PBBN corresponding to a C-DA.The address of the ingress node of the second PBBN may be the address ofthe ingress node per se, or may be the address of a port through whichthe data packet enters the node. Similarly, the address of the egressnode of the second PBBN may be the address of the egress node per se, ormay be the address of an egress port through which the data packet istransmitted from the edge node to the destination client network. Whenthe data packet arrives at the egress node of the second PBBN, the datapacket is decapsulated to remove the out MAC header and transmitted toanother client network.

Hereunder, an embodiment of the method and system for forwarding dataaccording to the present invention will be described in detail withreference to the accompanying drawings.

A network environment involved in the embodiment of the presentinvention is shown in FIG. 3. In that network, there are a plurality ofPBBNs established on the basis of 802.1ah. Each PBBN may be connectedwith several PBNs, and each PBN may be connected with several CustomerBridged Networks (CBNs). In addition, a PBBN may also be connecteddirectly with a CBN. Since the embodiment of the present inventionfocuses on a method for forwarding data between different PBBN domainsin a circumstance where a plurality of PBBNs are interconnected, allpossible PBNs and CBNs connected to a PBBN may be simplified as CBNs.These CBNs are connected to the PBBN through a User Network Interface(UNI) at the edge nodes of the PBBN, respectively. Different PBBNs areinterconnected through an External Network Network Interface (E-NNI) atthe respective edge nodes. In the embodiment of the present invention,since simply a data plane upon interconnection between domains isconsidered, only one path exists between any two networks, which can beimplemented by controlling protocol or managing plane, and the specificimplementation method is not considered in the present invention.

In order to achieve the object of the embodiment of the presentinvention, the provider first assigns a MAC address to each PBBN by anetwork manager as the provider network address. The provider networkaddress can uniquely identify a PBBN domain. A E-NNI interface at anedge nodes of each PBBN is statically configured with the networkaddress of the present PBBN by the network manager. In order todifferentiate from a MAC address of a bridge, a part of a MAC addressspace may be allocated to serve as a network address. For example, a MACaddress with first three bytes as “EE-CC-CC” can be allocated as anetwork address. Any other method can be used as long as a networkaddress can be differentiated from a MAC address of a bridge.

In a network environment where a plurality of PBBNs are interconnected,a PBBN includes a edge node and an intermediate node. The edge node isadapted to encapsulate/decapsulate a data packet with an outer MACheader, to establish mapping relationship between a C-SA and a B-SA, tostore the mapping relationship in a mapping table, and to performoperations such as address learning and forwarding table establishment.The intermediate node is adapted to establish a data forwarding table bymeans of address learning according to a source address and an ingressport in the outer MAC header of the data packet and to forward the datapacket according to the data forwarding table.

For a data packet transmission path, an edge node includes an ingressnode and an egress node. The ingress node is an edge node through whichthe data packet enters a PBBN from outside. The egress node is an edgenode through which the data packet exits the PBBN from the inside of thePBBN. The intermediate node is a node in the transmission path betweenthe ingress node and the egress node.

With reference to FIG. 4, FIG. 4 describes a PBBN network. PBBN_MACrepresents the provider network address corresponding to the PBBN. Thelines with an arrow represent the transmission path and transmissiondirection of the data packet in a PBBN when the data packet is forwardedbetween a plurality of PBBN domains. Ingress, Egress and Intermediaterespective represent an ingress node, an egress node and an intermediatenode corresponding to the service data flow in the PBBN. At Ingress andEgress, external interfaces directed to the present network include aUNI interface and an E-NNI interface, wherein the UNI interface ismainly adapted to handle data exchange with a client, and the E-NNIinterface is mainly adapted to handle data exchange with another PBBNnetwork. Usually, no data packet from the client network are received atthe E-NNI interface on the ingress node Ingress, otherwise it indicatesa wrong configuration. Similarly, the E-NNI interface on the egress nodeis not connected to the client network; otherwise it indicates a wrongconfiguration. Similarly, the UNI interface is not connected to anotherPBBN directly.

Hereunder, the processing flow of the data packet by respective edgenodes of a PBBN in the method for forwarding data according to thepresent invention will be further described in detail with reference tothe accompanying drawings.

At the ingress node (hereinafter referred to as Bridge) of a PBBN, aflow for processing a data packet received through the UNI interface areshown in FIG. 5. A flow for processing a data packet received throughthe UNI interface by an ingress node will be described in theembodiment. Under normal conditions, the data packet received throughthe UNI interface can only be a data packet transmitted from the clientnetwork. Therefore, the Bridge described in the embodiment is usually aningress node of a first PBBN into which the data packet from the clientnetwork enters. The processing flow shown in FIG. 5 includes thefollowing steps.

In step 501, address learning is carried out, and a data forwardingtable is established.

The address learning is to record the mapping relationship between theC-SA and the ingress port for the data packet at the Bridge into a dataforwarding table. In this step, the process of the address learning isidentical to self-learning mechanism of Ethernet network bridge in theconventional art, and therefore will not be described in detail here.

In step 502, the MAC address of the ingress port through which the datapacket enters the Bridge is used as the B-SA for the data packet,namely, the source address of the outer MAC header, and the processproceeds to step 503.

In this step, either the MAC address of the port through which the datapacket enters the Bridge or the MAC address of the Bridge can be used asthe source address of the outer MAC header.

In step 503, it is determined whether the corresponding B-DA is obtainedby looking up the mapping table of the present node according to theC-DA of the data packet. If the B-DA is obtained, the process proceedsto step 504. If the B-DA is not obtained, the process proceeds step 505.As mentioned above, an edge node needs to establish mapping relationshipbetween the C-SA and the B-SA by means of learning and store the mappingrelationship in a mapping table. The mapping relationship between theC-SA and the B-SA after learning can be used as the basis for queryingthe mapping relationship between the C-DA and the B-DA. In other words,after learning, the C-SA corresponds to the C-DA, and the B-SAcorresponds to the B-DA. Therefore, the corresponding B-DA can be lookedup in the mapping table between the C-SA and the B-SA after learningaccording to the C-DA in the data packet.

In step 504, the MAC address of the Bridge determined in step 502 isused as the B-SA, the data packet is encapsulated with an outer MACheader by using the B-DA obtained in step 503, and then the processproceeds to step 506.

Since the received data packet may be transmitted to another PBBN or maybe transmitted to a Bridge in the present PBBN, the destination MACaddress obtained by looking up the mapping table may be the address of aprovider backbone bridged network (PBBN) or the MAC address of a bridgeor Port in the present PBBN domain. If the B-DA obtained according tothe C-DA in step 503 is the network address of a certain PBBN, the PBBNis the PBBN that is directly connected to the destination clientnetwork, namely, the last PBBN in the PBBN network in which the datapacket is transmitted.

In step 505, the MAC address determined in step 502 is used as the B-SAand a first multicast address is used as the B-DA to encapsulate thedata packet with an outer MAC header, and forward the data packet to thepresent PBBN domain and all other adjacent PBBNs.

In this step, the first multicast address represents the UNI and E-NNIinterfaces at other edge nodes within the scope of the present network.

In step 506, an egress port is determined by looking up the dataforwarding table according to the B-DA in the data packet, and the datapacket is forwarded from the determined egress port. In addition to thelearning of the mapping relationship between the C-SA and the B-SA, eachedge node carries out the conventional learning the mapping relationshipbetween the MAC address and the port. Therefore, in this step, theegress port can be determined by looking up the data forwarding tableaccording to the B-DA in the data packet.

In the process of encapsulation of the data packet with an outer MACheader as described in steps 504 and 505, it needs to obtain the B-TAGaccording to the I-TAG in the data packet, and encapsulate with theI-TAG and B-TAG to obtain a complete PBBN data packet format. Thatprocess is identical to that in the conventional art, and will not befurther described in detail here.

The flow for processing the data packet at the E-NNI interface of theingress node Ingress of the PBBN network is shown in FIG. 6. Theprocessing flow described in the embodiment is the flow for processing adata packet received through the E-NNI interface at the ingress node.Under normal conditions, the data packet received from the E-NNIinterface is not a data packet transmitted from the client network, butusually is a data packet transmitted from another PBBN network.Therefore, the ingress node described in the embodiment is usually theingress node of an intermediate PBBN network and the last PBBN networkduring the transmission of the data packet from the source clientnetwork to the destination client network through a plurality of PBBNs.The processing flow shown in FIG. 6 includes the following steps.

In step 601, address learning is carried out and a data forwarding tableis established.

The address learning is mainly to record mapping relationship betweenthe C-SA and the ingress port for the data packet at the Bridge into adata forwarding table. In this step, the process of the address learningis identical to the self-learning of Ethernet network bridge in theconventional art, and therefore will not be described in detail here.

In step 602, it is determined whether the B-SA in the data packet is thenetwork address of the present PBBN. If the B-SA is the network addressof the present PBBN, the process proceeds to step 603; otherwise theprocess proceeds to step 604.

In this step, if the B-SA in the data packet received through theingress node is the network address of the present PBBN, it indicatesthat the data packet is transmitted from the present PBBN to anotherPBBN. In this case, a data packet loop is formed between the domains,and therefore the data packet is needed to be discarded.

In step 603, the data packet is discarded.

In step 604, it is determined whether the B-DA in the data packet is thenetwork address of the present PBBN. If the B-DA is the network addressof the present PBBN, the process proceeds to step 605; otherwise theprocess proceeds to step 609.

In step 605, the MAC address of the ingress port (namely, the ingressport through which the data packet enters the Bridge) or the MAC addressof the Bridge is used as the source address in the outer MAC header ofthe data packet (to replace the source address in the original outer MACheader), and the process proceeds to step 606. If it is determined instep 604 that the B-DA is the network address of the present PBBN,usually it indicates that the present PBBN is the last PBBN in thetransmission path to the destination client network, that is, thepresent PBBN is the PBBN that is directly connected to the clientnetwork.

In step 606, it is determined whether the corresponding B-DA is obtainedby looking up the mapping table of the present node according to theC-DA in the data packet. If the B-DA is obtained, the process proceedsto step 608; otherwise the process proceeds to step 607. As mentionedabove, the edge node needs to establish mapping relationship between theC-SA and the B-SA by means of learning and store the mappingrelationship in a mapping table. The mapping relationship between theC-SA and the B-SA after learning can be used as the basis for queryingthe mapping relationship between the C-DA and the B-DA. In other words,after learning, the C-SA corresponds to the C-DA, and the B-SAcorresponds to the B-DA. Therefore, the corresponding B-DA can beobtained by looking up the mapping table between the C-SA and B-SA afterlearning according to the C-DA in the data packet.

In step 607, the B-DA in the data packet is replaced with a secondmulticast address, and the data packet is encapsulated with an outer MACheader, and then the process proceeds to step 609. In this step, thesecond multicast address represents the UNI interface of other edge nodein the present PBBN domain.

In step 608, the destination address in the outer MAC header of the datapacket is replaced with the B-DA obtained in step 606. That is, the B-DAin the outer MAC header of the data packet is changed from the providernetwork address of the present PBBN to information of the B-DA obtainedin step 606. The information of the B-DA after the replacement isusually the address of the egress node through which the data packet istransmitted from the present PBBN to the destination client network (orthe address of the egress port through which the data packet istransmitted from the egress node to the client network), and then theprocess proceeds to step 609.

In step 609, the egress port is determined by looking up the dataforwarding table according to the B-DA in the data packet, and the datapacket is forwarded through the determined egress port.

If it is determined in step 604 that the B-DA in the data packet is notthe network address of the present PBBN and the process proceeds to step609, it indicates the PBBN (namely, the present PBBN) to which theBridge belongs is an intermediate PBBN (neither the first PBBN nor thelast PBBN) in the transmission path of the data packet. Therefore, theBridge can forward the data packet directly to a next hop according tothe mapping relationship between the MAC address (the B-DA) and the portthat is learned in the conventional forwarding table without anyprocessing of the outer MAC header of the data packet. On the contrary,if it is determined in step 604 that the B-DA in the data packet is thenetwork address of the present PBBN and the process proceeds to step609, it indicates the PBBN (namely, the present PBBN) to which theBridge belongs is the last PBBN in the transmission path of the datapacket. Thus the outer MAC header of the data packet is needed to beprocessed by step 607 or 608 before the data packet can be forwarded toa next hop in accordance with step 609, and then the data packet istransmitted to the destination client network after the outer MAC headeris removed at the egress node of the present PBBN.

As mentioned above, each PBBN has an ingress node, an egress node and anintermediate node. For an intermediate node in a PBBN domain, theprocess after a message transmitted from the ingress node is received isthe same as that defined in 802.1ah and 802.1ad and will not bedescribed here in detail. The process mainly includes the followingsteps.

In step 1, mapping relationship between the B-SA in the outer MAC headerof the data packet and the ingress port for the data packet is recordedin a forwarding table.

In step 2, the forwarding table is looked up to determine the egressport for forwarding the data packet according to the B-DA of the datapacket.

In step 3, the data packet is transmitted from the determined egressport.

The flow for processing a data packet at an ingress node involved in theembodiment of the present invention are described in detail above withreference to FIG. 5 and FIG. 6. Hereunder, the flow for processing thedata packet at an egress node will be described in detail with referenceto FIG. 7. The flow for processing the data packet at the egress node ofa PBBN domain is shown in FIG. 7. The process includes the followingsteps.

In step 701, address learning is carried out, and a data forwardingtable is established.

In this step, the address learning is to record mapping relationshipbetween the B-SA in the data packet and the ingress port for the datapacket in a data forwarding table.

In step 702, the forwarding table is looked up to determine a networkegress port for the data packet according to the B-DA in the datapacket, and the process proceeds to step 703.

In step 703, it is determined whether the egress port for the datapacket is a UNI interface. If the egress port is a UNI interface, theprocess proceeds to step 704 (it indicates that the PBBN to which thepresent node belong is the last PBBN in the data packet transmissionpath); otherwise the process proceeds to step 708 (it indicates the PBBNto which the present node belong is the first PBBN or an intermediatePBBN in the data packet transmission path).

In step 704, it is determined whether the B-DA in the data packet is theaddress of the egress port determined in step 702 by looking up theforwarding table. If the B-DA is the address of the egress port, theprocess proceeds to step 706; otherwise the process proceeds to step705.

In step 705, the data packet is discarded.

In step 706, the mapping relationship between the C-SA and the B-SA inthe data packet is stored in the data packet into a mapping table of thepresent node, and the process proceeds to step 707.

In step 707, the outer MAC header of the data packet is decapsulated,the data forwarding table is looked up according to the clientdestination address of the data packet to determine a client egressport, and then the data packet is transmitted to the client networkthrough the client egress port.

In step 708, it is determined whether the B-SA in the data packet is theprovider network address. If the B-SA is the provider network address,the process proceeds to step 711 (it indicates that the present PBBN isan intermediate PBBN in the data packet transmission path); otherwisethe process proceeds to step 709 (it indicates that the present PBBN isthe first PBBN in the data packet transmission path).

In step 709, the mapping relationship between the C-SA and the B-SA inthe data packet is stored in a mapping table in the present node.

In step 710, the B-SA in the data packet is replaced with the networkaddress of the present PBBN, and then the process proceeds to step 711.

In step 711, the data packet is forward to another PBBN from the networkegress port determined in step 702.

While the method for forwarding data between a plurality of PBBNs isdescribed above by means of the embodiments of the present invention,those skilled in the art shall note that a network to which theembodiment of the present invention is applicable include, but notlimited to, the fore-mentioned PBBNs, and the present invention can alsobe applied to a variety of provider Ethernet networks.

With reference to FIG. 8, FIG. 8 is a structural representation of anembodiment of the system for forwarding data between a plurality ofprovider Ethernet networks according to the present invention.

The system according to the embodiment includes a first providerEthernet network connected to a first client network and a secondprovider Ethernet network connected to a second client network. Thefirst provider Ethernet network is the first provider Ethernet networkin a path through which a first data packet is transmitted from thefirst client network to the second client network, and the secondprovider Ethernet network is the last provider Ethernet network in thepath through which the first data packet is transmitted to the secondclient network. There is no limitation on whether the first data packetpasses another provider Ethernet network (referred to as an intermediateprovider Ethernet network) during the transmission of the first datapacket forwarded from the first provider Ethernet network to the secondprovider Ethernet network. Since the intermediate provider Ethernetnetwork determines an inter-domain path by means of an existingself-learning mechanism (usually mapping relationship between a sourceMAC address and an ingress port), the structure of the intermediateprovider Ethernet network will not be described in detail here.Hereunder, the internal structure of the system will be furtherdescribed in combination with working principle of the system describedin the embodiment.

First, when a data packet transmitted from the first client network tothe second client network arrives at the first provider Ethernetnetwork, a first MAC header processing unit 81 carries out MAC headerencapsulation and replacement for the data packet according to a networkaddress of the first provider Ethernet network and a network address ofthe second provider Ethernet network. For the convenience ofdescription, hereinafter the data packet is referred to as a first datapacket. Specifically, first, an encapsulating sub-unit 811 at an ingressnode of the first provider network encapsulates the first data packetwith an outer MAC header. An address of the ingress node is used as thesource address in the outer MAC header and the network address of thesecond provider Ethernet network is used as the destination address inthe outer MAC header. Next, a first forwarding unit 83 forwards thefirst data packet encapsulated with the outer MAC header to an egressnode. Then, a first replacing sub-unit 812 at the egress node replacesthe source address in the outer MAC header of the first data packet thatis processed by the encapsulating sub-unit 811. The destination addressin the outer MAC header keeps unchanged, and the source address isreplaced with the network address of the first provider Ethernetnetwork. Then, the first forwarding unit 83 forwards the first datapacket processed by the first replacing sub-unit 812 to the secondprovider Ethernet network.

Now, the transmission process for the first data packet in the firstprovider Ethernet network is completed. It shall be noted that, in thefirst provider Ethernet network, a first learning unit 85 is furtherincluded. Similar to the first forwarding unit 83, the first learningunit 85 is disposed at respective edge nodes of the provider Ethernetnetwork. Specifically, the first learning unit 85 includes two learningsub-units. One of the two learning sub-units is configured to learnmapping relationship between a client source address and an ingress portin the data packet received at the present node. The other of the twolearning sub-units is configured to learn the client source address andthe source address in the outer MAC header in the received data packet.The first learning unit 85 provides required information for the firstMAC header processing unit 81 and the first forwarding unit,respectively. For example, the first learning unit 85 can provide thenetwork address of the second provider Ethernet network for theencapsulating sub-unit 811. That is, the first learning unit 85 queriesthe mapping relationship learned by the first learning unit 85 for thenetwork address of the corresponding second provider Ethernet networkaccording to the client source address of the first data packet. Inaddition, the first learning unit 85 can provide forwarding pathinformation for the first forwarding unit 83 according to the mappingrelationship between the client source address and the ingress port thatis learned by the learning unit. Since the first forwarding unit 83 anda second forwarding unit 84 that will be described hereunder can carryout forwarding by means of the existing self-learning mechanism, theforwarding process will not be described in detail here.

When the first data packet processed by the first MAC header processingunit 81 in the first provider Ethernet network arrives at the secondprovider Ethernet network, a second MAC header processing unit 82carries out replacement and decapsulation for the MAC header.Specifically, first, a second replacing sub-unit 821 at an ingress nodeof the second provider Ethernet network replaces the outer MAC header ofthe first data packet from the first provider Ethernet network. Thesource address in the outer MAC header after replacement is the addressof the ingress node of the second provider Ethernet network, and thedestination address is the address of an egress node of the secondprovider Ethernet network. Next, a second forwarding unit 84 forwardsthe first data packet encapsulated with the outer MAC header to theegress node of the second provider Ethernet network. Then, adecapsulating sub-unit 822 at the egress node of the second providerEthernet network carries out decapsulation for the outer MAC header ofthe first data packet that is processed by the second replacing sub-unit821, thereby an inner MAC header of the first data packet is obtained.Finally, after the decapsulating sub-unit 822 removes the outer MACheader from the first data packet, the second forwarding unit 84forwards the first data packet to the second client network. In thesecond provider Ethernet network, a second learning unit 86 whichprovides required information for the second MAC header processing unit82 and the second forwarding unit 84 is included. Since the secondlearning unit 86 is implemented in the same principle as the firstlearning unit 85, it will not be described again here.

The first provider Ethernet network and the second provider Ethernetnetwork described above each have a network address. In the systemaccording to the embodiment, a network address assigning unit can beused to assign a network address to each provider network and informrespective edge nodes at the provider Ethernet network. Of course, thenetwork address of each provider Ethernet network can also be configuredat an edge node of the provider Ethernet network manually. According toanother aspect of the present invention, the present invention furtherprovides an embodiment of another system for forwarding data betweenEthernet networks of a plurality of provider. The system according tothe embodiment includes a first client network, a second client network,a first provider Ethernet network, and a second provider Ethernetnetwork. The first client network is connected to the first providerEthernet network, and the second client network is connected to thesecond provider Ethernet network. The first provider Ethernet networkand the second provider Ethernet network are connected to each otherdirectly or via other provider Ethernet network (referred to as anintermediate provider Ethernet networks).

An edge node of the provider Ethernet network includes a mappingrelationship storage unit and an outer MAC header processing unit. Themapping relationship storage unit is adapted to store the mappingrelationship between the client source address and the source address inthe outer MAC header in the data packet received by the present node.Specifically, the mapping relationship storage unit can record themapping relationship by means of a mapping table. The outer MAC headerprocessing unit is adapted to replace the source address and thedestination address in the outer MAC header of the data packet accordingto the mapping information provided by the mapping relationship storageunit. If the first client network is to transmit a data packet (for theconvenience of description, hereinafter is referred to as a first datapacket) to the second client network, the first data packet at leastpasses through the first provider Ethernet network and the secondprovider Ethernet network (and may passes through an intermediateprovider Ethernet network between the first provider Ethernet networkand the second provider Ethernet network). The outer MAC headerprocessing unit at the egress node of the first provider Ethernetnetwork is adapted to replace the source address in the outer MAC headerof the data packet with the network address of the first providerEthernet network. The outer MAC header processing unit at the ingressnode of the second provider Ethernet network is adapted to query andobtain the address of the egress node of the second provider Ethernetnetwork corresponding to the client destination address of the datapacket according to the information provided by the mapping relationshipstorage unit, and to replace the source address and the destinationaddress in the outer MAC header of the data packet with the address ofthe ingress node and the address of the egress node of the secondprovider Ethernet network.

In addition, the edge node further includes an encapsulating unit thatis adapted to encapsulate the data packet transmitted from the clientnetwork with an outer MAC header and provide the data packet to theouter MAC header processing unit for use. Specifically, theencapsulating unit is the first encapsulating unit at the ingress nodeof the first provider Ethernet network, which is adapted to use theaddress of the present node and the network address of the secondprovider Ethernet network as the source address and the destinationaddress of the outer MAC header and encapsulate the first data packetwith the outer MAC header.

Of course, the edge node further includes a decapsulating unit, which isadapted to decapsulate the data packet transmitted from the clientnetwork and processed by the by the outer MAC header processing unit toremove the outer MAC header.

The edge node further includes a forwarding relationship storage unit,which is adapted to store mapping relationship between the sourceaddress in the outer MAC header and an ingress port of the received datapacket. Specifically, the mapping relationship storage unit can recordthe mapping relationship by means of a mapping table.

The edge node further includes a forwarding unit, which is adapted tolook up the mapping relationship provided from the forwardingrelationship storage unit and determine an egress port according to thedestination address of the data packet, and to transmit the data packetthat is encapsulated with the outer MAC header or decapsulated the outerMAC header through the egress port.

Furthermore, the edge node further includes a network address acquiringunit, which is adapted to acquire the network address of the providerEthernet network at the present node.

It can be seen from the embodiments described above that, theembodiments of the present invention utilize a network address of aprovider Ethernet network as an outer MAC header for data packettransmission between different provider Ethernet networks withoutinvolving an address of a specific edge node. Therefore, it isunnecessary to configure complex address mapping relationship atrespective edge nodes. An inter-domain path can be established simply bymeans of a self-learning mechanism to achieve transmission betweendomains, so that a data packet from a source client network is forwardedto a destination client network.

In addition, since the network address of the provider Ethernet networkused during the inter-domain transmission instead of the address of thespecific edge node is used as an outer MAC header for the data packetduring the inter-domain transmission, an address of a specific networkdevice (such as an edge node device) inside the provider Ethernetnetwork is not exposed to any other provider Ethernet network, whichenhances network security.

Moreover, in the embodiments of the present invention, a data packetfrom a client is encapsulated with only one layer of MAC header so thatforwarding between different provider Ethernet networks, which increasesforwarding efficiency.

The preferred embodiments of the present invention have been describedabove, and the scope of protection of the present invention is notlimited thereto. Any modifications and equivalent substitutions whichcan be easily conceived by those skilled in the art within the technicalscope of the disclosure of the present invention should be encompassedby the scope of protection of the present invention.

1. A method for forwarding data between a plurality of provider Ethernetnetworks, wherein a first provider Ethernet network is the firstprovider Ethernet network in a path through which a first data packet istransmitted from a first client network to a second client network, anda second provider Ethernet network is the last provider Ethernet networkin the path through which the first data packet is transmitted, whereinthe method comprises: using a network address of the first providerEthernet network and a network address of the second provider Ethernetnetwork as a source address and a destination address of an outer MACheader with which the first data packet is encapsulated when the firstdata packet is transmitted between the first provider Ethernet networkand the second provider Ethernet network; and decapsulating, by thesecond provider Ethernet network, the first data packet and forwardingthe decapsulated data packet to the second client network after thefirst data packet is forwarded to the second provider Ethernet network.2. The method according to claim 1, wherein when the first data packetis transmitted between the provider Ethernet networks, the using thenetwork addresses of the provider Ethernet networks as the sourceaddress and the destination address in the outer MAC header with whichthe first data packet is encapsulated comprises: encapsulating, by aningress node of the first provider Ethernet network, the first data packwith the outer MAC header by using the network address of the secondprovider Ethernet network as the destination address in the outer MACheader, and then forwarding the first data packet to an egress node ofthe first provider Ethernet network; and replacing, by the egress nodeof the first provider Ethernet network, the source address of the outerMAC header of the first data packet with the network address of thefirst provider Ethernet network, and forwarding the first data packet tothe second provider Ethernet network.
 3. The method according to claim2, wherein the decapsulating the first data packet and forwarding thefirst data packet to the second client network after the first datapacket is forwarded to the second provider Ethernet network comprises:replacing, by the ingress node of the second provider Ethernet network,the source address and the destination address of the outer MAC headerof the first data packet with an address of an ingress node and anaddress of an egress node of the second provider Ethernet network, andforwarding the first data packet to the egress node of the secondprovider Ethernet network after receiving the first data packet; anddecapsulating, by the egress node of the second provider Ethernetnetwork, the outer MAC header of the first data packet, and forwardingthe first data packet to the second client network.
 4. The methodaccording to claim 2, wherein the processing of the first data packet bythe ingress node of the first provider Ethernet network comprises: whenthe ingress node of the first provider Ethernet network acquires thenetwork address of the corresponding second provider Ethernet network byquerying learned mapping relationship according to client destinationaddress in the first data packet, encapsulating the first data packetwith the outer MAC header by using the address of the ingress node ofthe first provider Ethernet network and the network address of thesecond provider Ethernet network as the source address and thedestination address respectively, and then forwarding the first datapacket to the egress node of the first provider Ethernet network; andwhen the ingress node of the first provider Ethernet network cannotacquire the network address of the second provider Ethernet networkcorresponding to the client destination address by querying the learnedmapping relationship according to the client destination address of thefirst data packet, encapsulating the first data packet with the outerMAC header by using the address of the ingress node and a firstmulticast address of the first provider Ethernet network as the sourceaddress and destination address, and forwarding the first data packetencapsulated with the outer MAC header to other provider Ethernetnetworks connected to the first provider Ethernet network, wherein thefirst multicast address points to a user network interface and anexternal network network interface of the first provider Ethernetnetwork.
 5. The method according to claim 2, wherein the process of thefirst data packet by the egress node of the first provider Ethernetnetwork treats comprises: determining, by the egress node of the firstprovider Ethernet network, a forwarding egress port for the data packetaccording to the destination address of the outer MAC header of thefirst data packet; judging that the forwarding egress port is anexternal network network interface and the source address of the outerMAC header of the first data packet is not within network address scopeof the first provider Ethernet network; and replacing the source addressof the outer MAC header of the first data packet with the networkaddress of the first provider Ethernet network, and forwarding the firstdata packet towards the second provider Ethernet network.
 6. The methodaccording to claim 3, wherein the replacing and the forwarding by theingress node of the second provider Ethernet network comprises: if theingress node of the second provider Ethernet network determines that thedestination address of the outer MAC header of the first data packet isthe network address of the second provider Ethernet network, when theaddress of the egress node of the second provider Ethernet networkcorresponding to the client destination address is acquired by queryinglearned mapping relationship according to the client destination addressin the first data packet, replacing the source address and thedestination address of the outer MAC header of the first data packetwith the address of the ingress node and the address of the egress nodeof the second provider Ethernet network, and then forwarding the firstdata packet to the egress node of the second provider Ethernet network;when the ingress node of the second provider Ethernet network cannotacquire the address of the egress node of the corresponding secondprovider Ethernet network by querying the learned mapping relationshipaccording to the client destination address of the first data packet,using a second multicast address as the destination address of the outerMAC header of the first data packet and forwarding the first data packetto the client network connected to the second provider Ethernet network,wherein the second multicast address points to the user networkinterface of the second provider Ethernet network; and if the ingressnode of the second provider Ethernet network determines that thedestination address of the outer MAC header of the first data packet isnot the network address of the second provider Ethernet network, lookingup a forwarding table according to the destination address of the outerMAC header of the first data packet to determine an egress port, andforwarding the first data packet through the egress port.
 7. The methodaccording to claim 3, wherein the decapsulating and forwarding the firstdata packet by the egress node of the second provider Ethernet networkcomprises: looking up, by the egress node of the second providerEthernet network, a forwarding table according to the destinationaddress of the outer MAC header of the first data packet to determine anegress port; and decapsulating the outer MAC header of the first datapacket and forwarding the first data packet to the second clientnetwork, if the egress port is a user network interface and thedestination address of the outer MAC header is a MAC address of theegress port or the MAC address of the egress node.
 8. The methodaccording to claim 1, wherein the method further comprises: learning, byedge nodes of each of the provider Ethernet networks, the mappingrelationship between the client source address and the source address ofthe outer MAC header of the received data packet, wherein the mappingrelationship at least provides network address information of theprovider Ethernet network corresponding to the destination clientaddress for transmission between different provider Ethernet networks.9. The method according to claim 1, wherein the network address of theprovider Ethernet network is configured statically by a network managerto edge nodes of the provider Ethernet networks.
 10. The methodaccording to claim 1, wherein if the first data packet further passes atleast one intermediate provider Ethernet network between the firstprovider Ethernet network and the second provider Ethernet networkduring transmission of the first data packet forwarded from the firstclient network to the second client network, the method furthercomprises: determining, by the intermediate provider Ethernet network,an inter-domain path by means of a self-learning mechanism.
 11. A systemfor forwarding data between a plurality of provider Ethernet networkscomprising a first provider Ethernet network connected to a first clientnetwork and a second provider Ethernet network connected to a secondclient network, wherein the first provider Ethernet network is the firstprovider Ethernet network in a path through which a first data packet istransmitted from the first client network to the second client network,and the second provider Ethernet network is the last provider Ethernetnetwork in the path through which the first data packet is transmitted,wherein the first provider Ethernet network comprises: a first outer MACheader processing unit adapted to encapsulate the first data packet withan outer MAC header according to a network address of the first providerEthernet network and a network address of the second provider Ethernetnetwork; and a forwarding unit adapted to forward the first data packetprocessed by the first outer MAC header processing unit towards thesecond provider Ethernet network; the second provider Ethernet networkcomprises: a second outer MAC header processing unit adapted todecapsulate the outer MAC header of the first data packet from the firstprovider Ethernet network; and a second forwarding unit adapted toforward the first data packet processed by the second outer MAC headerprocessing unit to the second client network.
 12. The system accordingto claim 11, wherein the first outer MAC header processing unitcomprises: an encapsulating sub-unit at an ingress node of the firstprovider Ethernet network, adapted to encapsulate the first data packetwith the outer MAC header, wherein a source address of the encapsulatedouter MAC header is an address of the ingress node, and a destinationaddress of the encapsulated outer MAC header is the network address ofthe second provider Ethernet network; and a first replacing sub-unit atan egress node of the first provider Ethernet network, adapted toreplace the source address of the outer MAC header of the first datapacket processed by the encapsulating sub-unit, wherein the sourceaddress of the outer MAC header after the replacement is the networkaddress of the first provider Ethernet network.
 13. The system accordingto claim 11, wherein the second outer MAC header processing unitcomprises: a second replacing sub-unit at an ingress node of the secondprovider Ethernet network, adapted to replace the outer MAC header ofthe first data packet from the first provider Ethernet network, whereinthe source address of the outer MAC header after the replacement is anaddress of the ingress node of the second provider Ethernet network, andthe destination address of the outer MAC header is an address of anegress node of the second provider Ethernet network; and a decapsulatingsub-unit in the egress node of the second provider Ethernet network,adapted to decapsulate the outer MAC header of the first data packetprocessed by the second replacing sub-unit.
 14. The system according toclaim 11, wherein the first provider Ethernet network and the secondprovider Ethernet network each further comprise a learning unit atrespective edge nodes of the provider networks, respectively, adapted toprovide address information required for processing the first datapacket to rest units by carrying out address learning for the receivedfirst data packet.
 15. The system according to claim 14, wherein thelearning unit comprises: a first learning sub-unit, adapted to learnmapping relationship between a client source address and an ingress portof the received first data packet; and a second learning sub-unit,adapted to learn mapping relationship between the client source addressand the source address of the outer MAC header of the received firstdata packet.
 16. The system according to claim 15, wherein the learningunit provides the network address of the second provider required forencapsulating the first data packet with the outer MAC header for thefirst outer MAC header processing unit.
 17. The system according toclaim 11, wherein the system further comprises a network addressassigning unit, adapted to assign a network address to each of theprovider Ethernet networks and inform the edge nodes of thecorresponding provider Ethernet network.
 18. A system for forwardingdata between a plurality of provider Ethernet networks comprising afirst provider Ethernet network connected to a first client network anda second provider Ethernet network connected to a second client network,wherein the first provider Ethernet network is the first providerEthernet network in a path through which a first data packet istransmitted from the first client network to the second client network,and the second provider Ethernet network is the last provider Ethernetnetwork in the path through which the first data packet is transmitted,wherein an edge node of the provider Ethernet network comprises: amapping relationship storage unit adapted to store mapping relationshipbetween a client source address and a source address of an outer MACheader of the first data packet received by the edge node; and an outerMAC header processing unit adapted to replace the source address and adestination address of the outer MAC header of the first data packetaccording to mapping information provided by the mapping relationshipstorage unit; the outer MAC header processing unit at an egress node ofthe first provider Ethernet network is adapted to replace the sourceaddress of the outer MAC header of the first data packet with a networkaddress of the first provider Ethernet network; and the outer MAC headerprocessing unit at an ingress node of the second provider Ethernetnetwork is adapted to query and obtain an address of an egress node ofthe second provider Ethernet network corresponding to the clientdestination address of the first data packet according to informationprovided by the mapping relationship storage unit, and to replace thesource address and the destination address of the outer MAC header ofthe first data packet with the address of the ingress node of the secondprovider Ethernet network and the address of an egress node of thesecond provider Ethernet network.
 19. The system according to claim 18,wherein the edge node of the provider Ethernet network furthercomprises: an encapsulating unit adapted to encapsulate the first datapacket transmitted from a client network with the outer MAC header andto provide the first data packet to the outer MAC header processingunit; a decapsulating unit adapted to decapsulate the outer MAC headerof the first data packet that is transmitted to the client network andprocessed by the outer MAC header processing unit; a forwardingrelationship storage unit adapted to store mapping relationship betweenthe source address and an ingress port of the first data packet receivedby the edge node; and a forwarding unit adapted to query the informationprovided by the forwarding relationship storage unit according to thedestination address of the first data packet to determine the egressport, and to forward the first data packet that is encapsulated with theother MAC header or decapsulated the outer MAC header through the egressport.
 20. The system according to claim 19, wherein the encapsulatingunit is a first encapsulating unit at the ingress node of the firstprovider Ethernet network, which is adapted to use the address of theedge node and the network address of the second provider Ethernetnetwork as the source address and the destination address of the outerMAC header to encapsulate the first data packet with the outer MACheader.